Utilization of the Refrigeration Effect from LPG Expansion for a Refrigerated Display Cabinet (RDC): An Experimental Study of a Half-Cycle System

Energy demand for commercial refrigeration continues to rise alongside the global transition toward environmentally benign natural refrigerants, while conventional cooling systems for refrigerated display cabinets (RDCs) remain heavily dependent on electricity and synthetic refrigerants. This study investigates the utilization of the refrigeration effect arising from the pressure reduction of LPG (a propane-butane mixture) prior to combustion, known as a half-cycle refrigeration system, as an alternative cooling source for a small-scale (192 L) beverage RDC. Liquid LPG is expanded isenthalpically through an expansion valve into an evaporator placed inside the RDC, while the resulting LPG vapor is routed to a burner. Testing was conducted for 60 minutes with data logged at 1-minute intervals using PT100 RTD sensors, PSAN pressure transducers, and humidity sensors connected to an Autonics data acquisition system. Results show the system reaches quasi-steady state within ±10 minutes on the refrigerant side, with an actual cooling power of ±263 W based on the measured LPG mass flow rate (3.07 kg/h) and a specific refrigeration effect of ±309 kJ/kg. Although only ±1.23% of this cooling capacity was utilized as net RDC air energy reduction, indicating a substantial parasitic heat load from suboptimal insulation, the test RDC successfully reached the operating temperature range of commercial minimarket RDCs (5.4–8.3 °C, verified via thermal imaging) within the test duration. These findings thermodynamically demonstrate that the otherwise-wasted LPG refrigeration effect has potential as a supplementary (pre-cooling/auxiliary) cooling system for small-to-medium beverage RDCs, particularly for businesses that already consume LPG routinely, while pointing toward further research on insulation optimization and frost management for broader commercial application.